The invention relates to a rectangular coil having a plurality of turns which are located adjacent to one another and are composed of a superconductor in the form of a strip, which contains at least one core which is embedded in a normally conductive matrix material and is composed of high-Tc superconductor material. A corresponding coil is disclosed in WO 01/20756 A1.
In order to allow high-Tc superconductors in the form of a strip (referred to in the foreign text as HTS conductors) to be used in particular in rotating electrical machines, for example according to the WO-A1 document cited above, it is necessary for this conductor to be processed to form coils. Planar coil types are preferably used for this purpose, in particular of the so-called rectangular type. This should be understood as covering all coil types which at least approximately occupy a rectangular footprint, although they may also have rounded corners. Rectangular coils with rounded corners which each together at the end form semicircular curved parts, which may be connected by straight web parts, are also referred to as “racetrack coils”. In this case, appropriate coils are based on coils formed using known copper technology, which are intrinsically electrically insulated from the environment. Particularly because of the requirements for accelerator technology and magnetic-resonance technology, where stringent demands are placed on the field quality which allow errors only in the sub-ppm range for the current, standard superconducting racetrack coils have been used until now, which are produced by their conductors being electrically insulated within the individual turns, and electrically insulated from ground.
Known rectangular coils using HTS conductors in the form of a strip have until now been produced using insulated conductor material. At the moment, there are three normal methods for insulation, specifically:
a. lacquer insulation, for example a UV lacquer coating (see EP 1 075 030 A2),
b. a Capton-wrap sheath (see DE 38 23 938 A1), or
c. a PEEK extrusion coating (see WO 01/61712 A1).
However, appropriate methods are relatively complex, increase the production costs of the conductors, and conceal the risk of conductor damage.